1. Field of Invention
This invention relates to microelectromechanical system (MEMS) based structures and microelectromechanical system (MEMS) based systems including at least one bistable structure. This invention also relates to methods for fabricating such structures and systems, as well as methods for actuating microelectromechanical system based systems.
2. Description of Related Art
Bistable beams are known for use in microelectromechanical system (MEMS) based systems. Such bistable beams have applications in, for example, digital data storage and electrical and optical switching.
For example, a tunable micromechanical bistable system is described by M. T. A. Saif in xe2x80x9cOn a Tunable Bistable MEMSxe2x80x94Theory and Experimentxe2x80x9d, Journal of Microelectromechanical Systems, Vol. 9, No. 2, pp. 157-170, June 2000. The bistable system consists of a long slender micromechanical beam attached to an actuator. The beam is subjected to a transverse force at the middle and a residual stress developed during fabrication. The actuator generates a compressive force along the axial direction of the beam so that the beam buckles along the transverse direction into one of two equilibrium states.
Another example of a known beam structure is described by Vangbo et al. in xe2x80x9cA Lateral Symmetrically Bistable Buckled Beamxe2x80x9d, J. Micromech. Microeng., 8 (1998), pp. 29-32. As described, a lateral symmetrically bistable beam is snapped into the structure of a microelectromechanical system (MEMS) based device and held in a fixed position by spring forces. The beam structure consists of a released upright beam that has been oxidized to induce tensile stress or has a compressive film deposited thereon.
U.S. Pat. No. 6,168,395 to Quenzer et al. describes a bistable electrostatic actuator with pneumatic or liquid coupling. The bistable actuator has buckled membrane sections that are driven by enclosed electrodes. The membranes operate in counteraction, such that pulling one membrane down pushes the other membrane up. The bistable actuator is particularly designed for a microvalve application and uses curved-shaped electrodes.
U.S. Pat. No. 6,303,885 to Hichwa et al. describes a bistable micro-machined electromechanical switch. The bistable switch includes a switch element that is suspended between portions of a switch body by a plurality of spring arms that are attached at walls of hollow body portions of a center beam. The spring arms and hollow beam walls deform in response to a motive force of an actuator to move between the stable states.
As described above, either a built-in stress, an applied compressive force, or a hollow beam portion forming an additional spring is needed for known bistable beams. However, the addition of an actuator for the applied compressive force renders the design and fabrication of the system complex. Also, creating a built-in stress in a beam renders fabrication difficult because controlling the built-in stress is difficult. Further, the addition of a hollow beam portion increases the complexity of design and fabrication. This invention eliminates these and other drawbacks associated with conventional bistable beams.
The systems and methods according to this invention provide a micromachined bistable beam having a first stable state in which the beam is substantially stress-free.
The systems and methods according to this invention separately provide improved flexibility in the design of a bistable system.
The systems and methods according to this invention separately provide reduced complexity in the design of a bistable system.
The systems and methods according to this invention separately provide improved manufacturability of a bistable system.
The systems and methods according to this invention separately provide reduced size and weight of a bistable system.
The systems and methods according to this invention separately provide reduced manufacturing costs for a bistable system.
The systems and methods according to this invention separately provide bistable actuation with improved performance.
The systems and methods according to this invention separately provide bistable actuation with improved robustness and/or reliability.
The systems and methods according to this invention separately provide bistable actuation with improved efficiency.
The systems and methods according to this invention separately provide a bistable beam with increased out-of-plane stiffness.
The systems and methods according to this invention separately provide non-contact and/or steady state non-contact actuation of a bistable beam.
The systems and methods according to this invention separately provide switching using a bistable system.
The systems and methods according to this invention separately provide a waveguide switch with bistable actuation.
The systems and methods according to this invention separately provide attenuation using a bistable system.
The systems and methods according to this invention separately provide improved control of a first position of a bistable beam in its first stable state.
The systems and methods according to this invention separately provide improved control of a second position of a bistable beam in its second stable state.
The systems and methods according to this invention separately provide a bistable system including a stop that contacts a bistable beam when the beam is between first and second stable states and near the second stable state.
In various exemplary embodiments according to the systems and methods of this invention, a bistable microelectromechanical system (MEMS) based system comprises a micromachined beam having a first stable state, in which the beam is substantially stress-free and has a specified non-linear shape, and a second stable state. In various embodiments, the specified non-linear shape comprises a simple curve. In other various embodiments, the specified non-linear shape comprises a compound curve, such as, for example, four substantially identical arcs. In still other embodiments, the specified non-linear shape comprises a series of linear segments.
In various exemplary embodiments, the beam has at least one fixed boundary condition. In other various embodiments, the beam has at least one bearing boundary condition. In other various embodiments, the beam has at least one spring boundary condition. The beam may also have a combination of different boundary conditions.
In various exemplary embodiments, the system further comprises a stop disposed between the first and second stable states of the beam. The stop may be disposed near the second stable stated of the beam so that the beam is biased against the stop when moved from the first stable state.
In various exemplary embodiments according to the systems and methods of this invention, a bistable microelectromechanical system (MEMS) based system comprises: a micromachined beam having a first stable state, in which the beam is substantially stress-free and has a specified non-linear shape, and a second stable state; an actuator arranged to move the beam between the first and second stable states; and a movable element that is moved between a first position and a second position in accordance with the movement of the beam between the first and second stable states. The actuator may comprise one of a thermal actuator, an electrostatic actuator, a piezoelectric actuator and a magnetic actuator. In various exemplary embodiments, the actuator comprises a thermal impact actuator. In various other embodiments, the actuator comprises a zippering electrostatic actuator.
In various exemplary embodiments according to the systems and methods of this invention, a first force is applied in a first direction so that a micromachined beam having a first stable state, in which the beam is substantially stress-free and has a specified non-linear shape, is moved from the first stable state to a second stable state. Applying the first force may comprise applying a force using one of a thermal actuator, an electrostatic actuator, a piezoelectric actuator and a magnetic actuator. In various exemplary embodiments, applying the first force comprises applying a force using a thermal impact actuator. In various other embodiments, applying the first force comprises applying a force using a zippering electrostatic actuator.
In various exemplary embodiments, a second force is applied in a second direction so that the beam is moved from the second stable state to the first stable state. Applying the second force may also comprise applying a force using one of a thermal actuator, an electrostatic actuator, a piezoelectric actuator and a magnetic actuator. Applying the second force may also comprise applying a force using a thermal impact actuator or using a zippering electrostatic actuator.
In various exemplary embodiments according to the systems and methods of this invention, a bistable microelectromechanical system (MEMS) based system is fabricated by lithographically defining a beam having a specified non-linear shape corresponding to a first stable state of the beam. In various exemplary embodiments, the fabrication method further comprises determining a second stable state of the beam by lithographically defining the beam to have a certain geometry. In various embodiments, lithographically defining the beam to have a certain geometry comprises lithographically defining the beam to have at least one of a certain length, a certain width, a certain height and a certain curvature. In various embodiments, the height of the beam is defined to be greater than the width of the beam to reduce potential out-of-plane buckling of the beam.
In various exemplary embodiments, the fabrication method further comprises determining a throw distance of the beam between the first and second stable states by lithographically defining the beam to have a certain geometry. In various embodiments, lithographically defining the beam to have a certain geometry comprises lithographically defining the beam to have at least one of a certain length, a certain width, a certain height and a certain curvature.
In various exemplary embodiments, the fabrication method further comprises determining a force curve of the beam between the first and second stable states by lithographically defining the beam to have a certain geometry. In various embodiments, lithographically defining the beam to have a certain geometry comprises lithographically defining the beam to have at least one of a certain length, a certain width, a certain height and a certain curvature.
In various exemplary embodiments, the fabrication method further comprises forming at least one of a thermal actuator, an electrostatic actuator, a piezoelectric actuator and a magnetic actuator adjacent the beam. In various embodiments, forming at least one of a thermal actuator, an electrostatic actuator, a piezoelectric actuator and a magnetic actuator adjacent the beam comprises forming a thermal impact actuator. In various other embodiments, forming at least one of a thermal actuator, an electrostatic actuator, a piezoelectric actuator and a magnetic actuator adjacent the beam comprises forming a zippering electrostatic actuator.
In various exemplary embodiments, the fabrication method further comprises forming at least one fixed boundary condition of the beam. In various other embodiments, the fabrication method further comprises forming at least one bearing boundary condition of the beam. In various other embodiments, the fabrication method further comprises forming at least one spring boundary condition of the beam. The fabrication method may further comprise forming a combination of different boundary conditions of the beam.
In various exemplary embodiments, the method step of lithographically defining the beam comprises patterning the beam in a device layer of a silicon-on-insulator wafer. The fabrication method may further comprise partially etching an insulator layer between the device layer and a substrate to release the beam with part of the insulator layer remaining to anchor the beam to the substrate.
In various exemplary embodiments according to the systems and methods of this invention, a microelectromechanical system (MEMS) based system comprises an input, an output, a movable element communicating between the input and the output and a micromachined beam having a first stable state, in which the beam is substantially stress-free and has a specified non-linear shape, and a second stable state. In various exemplary embodiments, the system is an optical system having an optical input and an optical output. In other exemplary embodiments, the system is an electrical system having an electrical input and an electrical output. In still other embodiments, the system is a fluidic system having a fluidic input and a fluidic output. In various exemplary embodiments, the system comprises a data storage system. In other exemplary embodiments, the system comprises a switching system.
These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the systems and methods according to this invention.